Comparator control for a tumbling drier



March 17, 1954 H. T. THUNANDER 3,125,422

COMPARATOR CONTROL FOR A TUMBLING DRIER 2 Sheets-Sheet 1 Filed Oct. 13, 1959 FIG I PO WZR Q sognc:

SENSOR I I 2 3-0 lull/1111112 3s l5 l5 ND/C 7'05 A fi 77ME pzmv Mir/WW9! 32 r HEATED PLATE '1 mvzm'oa HANS T. THUNANDER v ATTORNEY.

. exhaust air, etc.

United States Patent 3,125,422 COMPARATOR CONTRGL. FOR A 'TUMBLING Damn Hans T. ,Thnnander,.Mansfield, Ohio, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania 'Filed Get. 13, 1959, Ser. No. 846,098 -7 Clairns. (Cl. 34-45) This invention relates to control mechanism, particularly to mechanism for measuring the dampness or moisture content of a material, and has for an object to provide improved mechanism of this character.

the clothes to dry. A thermostat may be utilized and can be so located within the dryer as to respond fairly well to a. completely dry condition, but insofar as applicant is aware there is no reliable device .on the market to automatically shut off the dryer when the clothes are .still damp enough for ironing. Such a control is a very desirable feature for a dryer, and many attempts have been made to design such a control. Insofar as applicant ,is aware, all such attempts have been based on the fact that,-.as the clothes dry below a certain moisture content, the rate of drying falls off. This in turn is reflected in various phenomena in the dryer, .such as exhaust temperature, heat utilized for vaporization, humidity in the A relatively large number of seemingly unrelated control schemes are based on this fundamental principle, and efforts have been directed at finding qualitiessuch astempe-rature, time, etc., and combinations of qualities, which respond as purely as possible to the rate of drying. Unfortunately, .most of these qualities also respond to ambient temperature, line voltage, load size, air flow, initial amount of water present in the clothes, heating and cooling of dryer parts, etc. Such controls,although not infeasible, tend to be either inadequate, or cumbersome and expensive. "l hefundamental principle is not entirely correct either. For instance, the, correlation between rate of drying and moisture content is not the same for heavy fabrics as for light fabrics, nor for cotton as for rayon or nylon.

The; dryer control of the present invention utilizes an entirely new approach based on a principle which is independent of the drying process and of the dryer. It is based on measurement of the cooling effect of the clothes on a heated body. As thismeasurement is independent of whether or not the clothes are drying, most of the variables that render the previously mentioned control vschemes unsatisfactory are eliminated.

In accordance with the invention, there is provided a-pair of bodies or plates, together with means for heat- -;ing on.e of the plates. The plates are positioned within cooled by the damp clothes as the latter are tumbled in the dryer basket. The invention may be practiced (a) bysupplying a constant amount of heat to the heated plate. and measuring the difference in temperature of the twoplates, (b) by supplying sufficient heat to the heated plate to maintain a predetermined difference in the temperatures of the two plates and measuring the heat or power input required to maintain the predetermined temperature difference, or (c) by varyingboth the power input and the temperature difference of the two plates.

It is believed obvious that in the early portion of a drying cycle the clothes will have a relatively high moisture content and,hence, high heat conductivity, with the result that much of the heat supplied to the heated plate will be removed therefrom by the clothes. As the clothes approach damp dry or dry condition, the moisture content thereof will be relatively low and the heat conductivity correspondingly low, with the result that a greatly decreased heat input to the heatedplate will be sufficient to maintain the predetermined temperature difference of the two plates, or, where .a fixed amount of heat is supplied to the heated plate, the temperature differenee between the two plates will increase greatly. Such decrease in heat input or increase in temperature difference is readily measured and utilized to control the drying cycle, as, for example, by effecting an audible or visual signal or terminating supply of drying'heat to the basket and the clothes therein when the clothes have reached the desired degree of dryness.

In a preferred form of the invention, each plate'has associated therewith a thermally responsive device responsive to its temperature. The thermally responsive devices, for example, bimetals which have matched deflection, are arranged to keep a pair of contacts closed normally, but When the heated plate is, for example, 30 hotter than the unheated plate, the contacts open and interrupt heating of the heated plate. The unheated plate assumes a temperature close to that of the clothes and hence may be termed a reference plate. The contacts which control the plate heater will cycle and allow enough heat to develop in the heated plate to maintain the temperature thereof 30 F. above the clothes temperature as measured by the reference plate. The power required for this is a function of the cooling ability of the clothes, which, in turn, depends on the amount of Water at the surface of the clothes. When the clothes are wet, the heat conductivity thereof is considerably greater than when they are dry and, therefore, the heat loss from the heated plate is greater and the contacts are closed during a greater percentage of the time.

Another phenomenon of a different nature, but with the same effect, is also present. The cooling mass of the clothes, which draws heat from the heated plate, consists of the fibers of the clothes plus the water contained therein. Wet clothes, therefore, present a greater heat capacity than dry clothes, as well as a difference in conductivity. Inasmuch as the clothes are in definite con tact with the plates during only a relatively short portion of the total time, the heat capacity becomes an important factor and may, in fact, be the dominating one.

Yet another characteristic of most fabrics, which varies directly with the dampness or moisture content thereof, is that of softness or flexibility. When fabrics are very damp they have a high degree of flexibility permitting them to deform to closely contact or engage any surface against which they rest. As they dry and their moisture content decreases their softness or flexibility also decreases and their stiffness increases with the result that their contact With any supporting surface is less intimate.

The previously described pair of plates, heater, bimetals and contacts may be termed a sensor, since they sense the moisture content of the clothes. Similarly, the invention includes what may be termed a responder, that is, a device which responds to the action of the sensor and may be located remotely with respect thereto. The responder includes a bimetal and a heater therefor which is in series with the sensor heater and will, therefore, receive power in a fixed ratio with the sensor heater. As the responder bimetal is heated, its resulting deflection is a function of the dampness of the clothes. This responder bimetal may be arranged to perform any of a number of functions; for example, indicate dampness on a dial, sound an alarm, shut off the main heater of the dryer, etc.

An object of the invention is to measure the dampness of fabrics or clothes during drying of the same.

' ing operation.

A further object of the invention is to control a clothes dryer in response to the dampness or moisture content of the clothes being dried.

Another object of the invention is to continuously measure the dampness of clothes as they are dried in a clothes dryer and to reduce the supply of drying heat to the clothes during the cycle or to terminate the supply of drying heat to the clothes when the clothes have attained the desired degree of dampness or dryness.

The above and other objects are eifected by the invention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

FIG. 1 is a transverse sectional view taken through one form of clothes dryer controlled in accordance with the present invention;

FIG. 2 is an enlarged transverse sectional view through one form of dampness measuring device constructed in accordance with the present invention and utilizable in a dryer such as shown in FIG. 1, the electrical circuit for the device being shown schematically;

FIG. 3 is a perspective of the dampness measuring device of FIG. 2;

FIG. 4 is a chart illustrating a principle utilized in the present invention;

FIG. 5 is a plan view showing a modified and refined dampness control;

FIG. 6 is a transverse sectional view, taken along the line VI-VI of FIG. 5, looking in the direction indicated by the arrows, and including a schematic showing of a portion of the control mechanism;

FIG. 7 is a transverse sectional view taken along the line VII-VII of FIG. 5; and,

FIG. 8 is a schematic view of a further modification of the invention.

Reference will now be had to FIG. 1 of the drawing, wherein the invention is disclosed applied to a clothes dryer of the domestic type and of generally conventional construction. This type of dryer usually includes a casing structure 10 having a generally cylindrical bafiie 11 arranged therein and enclosing a drying chamber 12. The drying chamber is provided with an air inlet duct 13 for conveying heated air to the chamber 12 and an air discharge duct 14 for conveying vitiated moist air therefrom. A generally cylindrical basket 15 is arranged within the drying chamber 12 and is mounted for rotation about a horizontal axis. It will be understood that the cylindrical side wall of the basket is perforate substantialy throughout its circumferential extent for the passage of air translated from the air inlet duct 13 throughout the basket 15 to the discharge duct 14. Preferably, the basket 15 is provided with a plurality of radially inwardly extending vanes 16 for tumbling the clothes during the dry- The casing 10 and the basket 15 have conventional. registering openings (not shown) formed therein for providing access to the interior of the basket for insertion and removal of clothes.

The basket is suitably journalled in the casing 10 for rotation about a horizontal axis and is driven by a sheave 17 belted, as shown at 18, to an electric motor 19 supported by the bottom of the casing 10. The motor 19 also functions to drive a blower rotor 21 arranged within a blower housing 22. The latter is provided with an air inlet opening 23 communicating with the space within the casing 10, which space receives air from the surrounding atmosphere through openings (not shown) formed in the casing side wall. The blower housing 22 discharges into the air inlet duct 13 within which an electric heater 26 of suitable construction is disposed for heating the air discharged by the blower rotor 21. The heated air passes through the duct 13 to the drying chamber 12 and thence to the interior of the basket 15 for contacting the tumbling clothes and for the vaporization of water therein. The vitiated air and the water vapor absorbed thereby pass to the discharge duct 14.

The structure so far described may be considered as conventional, and the present invention is utilized in a novel control for a dryer of any conventional type, typified by the above-described dryer.

The rather basic form of the invention herein illustrated in FIGS. 2 and 3 comprises a dampness measuring device 3'8, hereinatter referred to as a sensor inasmuch as it is utilized to sense the dampness or moisture content of the clothes being dried. The sensor 30 includes a casing 31, preferably of poor heat conducting material, having bottom and side walls and having its open top closed by plates 32 and 33, preferably of metal or other material having good heat conducting characteristics. The plates 32 and 33 are electrically separated by a gap 34 which is covered by suitable means, such as a strip 36 of adhesive tape or the like. The plates are insulated from the sensor casing 31 by a seal 37 of felt, foam plastic, or other material having low heat conductivity and may be re t ained in covering relation to the casing 31 by any suitable means, for example, an adhesive connection between the plates and the seal 37. The primary purpose of the seal 3-7 is to prevent entry of dust to the casing 31.

The plate 32 has associated therewith an electric heater 38 for raising the temperature of the plate (hereinafter referred to as the heated plate, the other plate 33 being hereinafter referred to as the reference plate). The heater 38 receives electrical energy from the secondary of a transformer 39 via the conductor 41. The heated plate has a main thermally responsive member in the form of a bimetallic arm 42, and the reference plate similarly has a reference thermally responsive member in the form of a bimetallic arm 43. These bimetallic arms are adapted to be deflected by heat conducted thereto from their respective plates by U-shaped supporting brackets 44 which carry adjusting screws 46 by which the bimetallic arms 42 and 43 may be adjusted relative to each other.

The bimetallic arms carry cooperating contacts 47 which, when engaged, provide a circuit from the secondary of the transformer 39 through conductor 41, plate heater 38, a conductor 48 which has a few turns wrapped around the bimetallic arm 42. to provide a heater 49* for a purpose to be hereinafter explained, the bimetallic arm 42, the contacts 47, the bimetallic arm 43, the bracket 44, the reference plate 33 and conductor 51.

The bimetallic arms 42 and 43 have matched deflection and are arranged to maintain the contacts 47 normally plate. In operation, the reference plate assumes a temperature close to that of the clothes and the contacts, which control the heater 38, will cycle and allow sufficient heat to develop in the heater to elevate the temperature of the heated plate to approximately 30 F. above the temperature of the reference plate and of the clothes. Hence, the power input to the heater 38 is, in elfect, a function of the cooling ability of the clothes, which in turn depends on the amount of water at the surface of the clothes. When the clothes are wet, as in the early portion of a drying cycle, the heat conductivity thereof is considerably greater than during the latter portion of the drying cycle when they are only slightly damp or nearly dry and, therefore, the heat loss from the heated plate 32 is greater during the initial portion of the dry ing cycle and the contacts 47 are closed during a greater percentage of the time. As the drying of the clothes proceeds, less and less power input to the heater 38 is required to maintain the selected temperature difference (30 F.) between the heated and reference plates.

The contacts 47 which control the power input to the heated plate 32 also control the power input to a responder 52 which may be located at any remote position relative to the sensor 30. In the construction herein illustrated, the responder 5 2 is preferably located in the upper right-hand corner of the dryer casing 10.

'5 The-responder 52 includes a heater 53' wrappedabout, or disposed in close proximity to, an ambient compensated bimetal 54. The responder heater 53 is connected in series with the sensor. heater 38, between the conductor 51 and an additional conductor '55 connected to the secondary of the transformer 39. Since the responder heater 53 is in the same circuitwith the sensorheater 38, it is energized at the same times as the latter. Consequently,

the responder bimetal 54 is heated most of the time durmoves a contact 56 carried thereby into engagement with a mating contact 57 carried -:at the free end of a resilient arm 58. Cooling of the responder fbimetal at the end of the drying cycle separates'the contacts 56, '57. The arm 58 is provide-dwit-h a cam follower 59 maintained in engagement, through the natural resiliency of the arm '8, with a cam 61 mounted on a shaft-dz'carryingat its tree end a control knob 63 by whichthe user may adjust theposition of contact 57 relative'to contact 56-. Ad-

. justment of the-position of contact 57 relative to, contact '56 will vary the degree of dryness of the clothesat which the contacts disengage to open a circuit provided by a pair oi conductors 64 and 65. Opening of this circuit may effect any ofseveral functions such as energizing analarm signal, operating a visual indicator, interrupting the electrical circuit to the main heater 26 of the dryer, etc.

It should be noted that the power to the responding 'bimetal 54 is-receding during the dryinglcycle and consequently, inwa simple responding device as herein disclosed, the contacts 56 and 57 will be open during a warmup period of the control when the dryer is firstst-arted and until current has flowed through the circuit to the sensor and responder heaters for the majorv portion of a minute to heat the responder bimetalsufliciently to close the contacts 56 and57. In order tokeep the dryer operating during this first minute or less of operation-of the dryer, any ofseveral expedients may be utilized, for example, a resettable latch which the bimetal 54 can release only when moviug in the'oooling direction, or a simple time delay mechanism which will maintain the air heater 26 energized. until after the contacts 56 and 57 of the responder engage.

-In order to speed up the cycling of the sensor-30, the small heater 49, provided by the several Wrappings, of the conductor 4-55 about the bimetallic arm 32, may be utilized.

Thisresults in the temperature control becoming a proportioning control with the cycling rate essentially independent of .the response time of the heated plate-and its heater. This rapid cycling of the contacts 47 in the I sensor willreduce oscillation of the. responding bimet-al FIGS. 5 to 7 illustrate an improved sensor construction, operating in much the same ntaimer as thesensor v3t previously described .in connect-ion with FIGS. 1 to 3 penature is assumed and all edge and end effects. are ignored. 'I'henithe temperature distribution from endto end in the plate will be as shown by curve A. --N ext, it is .coefiicient is lat-proportionality factor. that expresses the .nssume-d that theplate is cooled andthe temperature .at

the heated end of the plate is maintained the same. The temperature distribution in the plate is as shown by curve B. Finally, assume that the thermostatis utilized to, control the heat input to maintain the temperature. at the cool end of the plate at its original level. The temperature distribution will now be as shown by curve C. By the choice .of thepnoper constants for the system, theelectrical energy consumption can be made to increase at .a considerably greater rate than the cooling coefficient. The cooling heat loss through one unit of heated plate area tor one unit of temperature difierence during "one unit of time. Within the limitations presented by the dampness control of the present invention, an increase in energy consum tion of two and a half percent for each percent increase in cooling coefficient is obtained.

The edge and end efiects may be reduced by symmetrical designfor instance, a plate or rod heated at the center with the thermostat at one end, or may besubstantially eliminated by use of a disc with the heater arranged .around the edgeand the thermostat at the center.

The last-mentioned arrangement is utilized in the improvedsensor 70, illustrated in FIGS. 5, 6 and 7, wherein the heated plate 71 is in the form of a disc of thin metal,

tor instance nickel plated steel .005 inch in thickness, and

slightly domed for strength.

The disc is provided with a cylindrical peripheral flange 7.2 for added strength and rigidity and also for supporting a sensor heater 73 which, in the construction illustrated, constitutes one or more turns about the flange of a resistance wire insulated with glass fibers and impregnated with a silicone resin. It is held to the plate flange by an epoxy adhesive compound. The heated plate or disc71 is positioned in a circular opening provided at the center of a rectangular reference plate '74, which also may be of nickel plated steel, disposed in covering relation to a casing 76 of electrically insulating material. The disc and rectangular reference plate are electrically and thermally soldered or brazed to the under surface of the heated plate.

A nut clamps the bimetal 81 against the lower end of the bushing '83, the latter providing good-heat flow from the heated plate to the bimetal since it is metallic.

Due to the thinness of the heated plate, there is a high temperature gradient therein from the region of the heater 7 3 to the main bimetal 81.

The screw is of sufiicient length to permit threaded attachment to the lower end thereof of an insulating bushing '85 which serves to support a yoke v86of resilient material,

.the latter being held against the bushing by a screw 87.

As best shown in FIGS; 5 and 7, the yoke 86 has legs 88 bearing against the inner surface of the rectangular reference plate '74, thereby holding the heated plate or .disc 71,

the supporting ring 77 and the reference plate 74 in assembled relation as a unit.

The reference plate 74 carries a reference'bimetal89 andjbothg the main bimetal 81 and the reference bimetal 39 are relatively short to provide for fast response. Both 'bimetals 81 and 89 are extended by rigid bars 91 and 92,

respectively, the former carrying a contact93 and the latter carrying a mating or cooperating contact 94 provided by the rounded point of an adjusting screw carried by the bar 92 on the responder bimetal 89. vSince both the heated and the reference plates, the insulating ring therebetween, and the bimetals and their associated contact structures .are all retained assembled as a unit by the yoke86, they are completely independent of the sensor casing 76 and consequently warpage or thermal expansion bimetal tends to engage the contacts.

of the latter cannot interfere with calibration of the bimetals and their contacts;

The bimetals 81 and 89' and their respective extension bars 91 and 92 are designed so that the deflection at the contacts is equal and in the same direction for the same change in temperature. Heating of the main bimetal alone causes movement of its contact 93 in the direction of opening of the contacts, while heating of the reference Preferably, the calibration is such that the contacts will open when the center of the disc or heated plate 71 is approximately 30 F. warmer than the reference plate 74, assuming there is no gravitational effect. Actually, the effect of gravity is relied upon to cause one bar and its contact to deflect more than the other. The calibration screw on the reference bimetal bar 92 serves, in addition to providing for relative adjustment of the contacts, to weight that bimetal. Consequently, when the dryer basket rotates, the calibration is cyclically changing around the average 30 F. temperature difference by about 10 F. to each side of the 30 F. averagei.e., between F. and 40 F., approximately. When the temperature difference is within this range, the contacts will open and close once during each revolution of the basket. The percentage of closed contact time, or on time, will vary from 100% at 20 F. to 0% at 40 F.

The above-described construction for producing cycling, which is generally the equivalent of the heater 49 of FIG. 2 provided by a few turns of conductor 48 about bimetal 42, is much simpler and cheaper than the latter and yields rapid cycling with positive make and break.

The ambient temperature in the dryer changes, some times quite rapidly, and the two sensor bimetals must have closely the same speed of response. In the presently Ydescribedconstruction both bimetals and bars are identical. However, the sensor disc 71 and reference plate 74 have different properties as the former is preferably of the order of .005 inch thickness and the latter may have a thickness of .050. By providing a reference plate which is thinner at the point where its bimetal is spot welded thereto, the two responses can be made sufiiciently similar.

As best shown in FIG. 6-, the responder 52 and the circuitry for the responder and the sensor 70 are the same as previously described in connection with the control of FIG. 2. Both controls operate in the same manner. Consequently, any description of the operation of the control of FIGS. 5, 6 and 7 is omitted to avoid repetition.

It will be noted that the two sensor arrangements previously described both operate by maintaining a constant temperature difference between the heated plate and the reference plate and measuring the change in power input to the heated plate required to maintain this constant temperature difference. As mentioned earlier, the invention also may be utilized by maintaining the input to the heated plate constant and measuring the gradual increase in temperature difference between the two plates as drying of the clothes progresses. One possible arrangement for such a control is illustrated schematically in FIG. 8.

In this figure a sensor (shown schematically at 130) is provided which may be generally similar in structure to the sensor 30 of FIG. 2 or to the sensor 70 of FIGS.

' 5, 6 and 7. If it is of the latter type, utilizing a disc, such disc should no longer be thin relative to the reference plate, or at least should have much better heat conductivity since a temperature gradient in the disc is not desirable in a constant power input control.

reference plate of, for example, 30 F., and the wattage in the disc heater is adjusted in any of several ways; for example, by adjusting the voltage output of a voltage regulator if the latter is of the variable type, by adjusting a rheostat 101, or by changing the magnitude of the current in the sensor heater by any conventional method.

The responder includes a compensated bimetal 1'54 and heater 153 whose energization is controlled by the sensor contacts 47. The responder bimetal contact 56 engages a contact 157 provided by the point of a calibrati-on screw 106 threadedly mounted in a fixed support 107 which also serves as a terminal for conductor 64.

In this arrangement the responder functions primarily as a relay to cut off heat to the main dryer heater 26, or to signal completion of the drying cycle. Selection by the user of a desired degree of dampness of the clothes at which the drying cycle is terminated is effected by varying the wattage input to the sensor heater, by one of the means proposed above.

Inthe operation of this embodiment of the invention, the apparatus is started as in the previously-described controls. As drying progresses, the cooling effect of the damp clothes on the sensor heated plate decreases and the temperature difference between the heated and reference plates increases until it is approximately 30 F. At

this point the sensor contacts 47 separate and the responder heater 153 is deenergized and its associated bimetal 154 cools until the contacts 56 and 157 separate to interrupt the circuit through conductors 64 and 65 controlling the main heater 26, or operating a signal, or some appropriate function.

While the invention has been shown in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

What is claimed is:

1. In mechanism for measuring a condition of a material tumbling in a container, which condition affects the heat absorpion characteristic of the material, two bodies adapted to be contacted and cooled by the tumbling material, an electrical heater for one of the bodies, means providing an electrical circuit for the heater, means for controlling said electrical circuit including a main thermally responsive member associated with the body having the heater and being responsive to the temperature thereof, a reference thermally responsive member associated with the other body and being responsive to the temperature thereof, cooperating contacts carried by said thermally responsive members for opening and closing said electrical circuit, said thermally responsive members normally maintaining the contacts in circuit-closing engagement and separating said contacts only when the temperature difference of the two bodies sensed thereby exceeds a predetermined value, a responding thermally responsive member, means operable by said responding thermally responsive member, and an electrical heater in the circuit for heating said responding thermally responsive member when said circuit is closed.

2. 'In mechanism for measuring the moisture content of fabric tumbling in a container; a pair of plates adapted to be contacted and cooled by the tumbling fabric, one of said plates being relatively thin; an electric heater for the thin plate; means providing an electrical circuit for said heater; means for controlling said circuit including a main thermal-1y responsive device responsive to the temperature of the thin plate and disposed in spaced relation to the heater for said thin plate, said thin plate having a high temperature gradient between its heater and its thermally responsive device, a reference thermally responsive device responsive to the temperature of the other plate, cooperating contacts controllable'by said thermally responsive devices into and out of circuit-clos- .9 ing engagement, at responding thermally responsive device, an indicator operable'by the responding thermally responsive device, and an electrical heater in said circuit for heating said responding thermally-responsive device when said circuit is "closed.

3. For use with a clothes dryer having a basket for tumbling damp clothes to be dried, means for supplying heat to the basket, means for rotating the basket, control mechanism for terminating the supply of heat to the basket in response to reduction of the moisture content of the clothes to a preselected value, said control mechanism comprising: a pair of plates adapted to be contacted and cooled by the clothes as the basket is rotated, electrical means for heating one only of said plates, means providing an electrical circuit for the plate heating means, a pair of contacts in said circuit movable into and out of circuit-closing engagement, a main thermally responsive member for moving one of said contacts in response to changes in temperature of the heated plate, a reference thermally responsive member for moving the other of said contacts in response to changes in the temperature of the other plate, an electrical device for controlling the supply of heat to the basket, a responding thermally responsive member for controlling said electrical device, and a heater for the responding thermally responsive member in the electrical circuit in series with the electrical heating means for the heated plate.

4. For use with a clothes dryer having a basket for tumbling damp clothes to be dried, means for supplying heat to the basket, and means for rotating the basket, control mechanism for terminating the supply of heat to the basket in response to reduction of the moisture content of the clothes to a preselected value, said control mechanism comprising: a pair of plates adapted to be contacted and cooled by the clothes as the basket is rotated, electrical means for heating one only of said plates, means providing an electrical circuit for the plate heating means, a pair of contacts in said circuit movable into and out of circuit-closing engagement, a main thermally responsive member for moving one of said contacts in response to changes in temperature of the heated plate, a reference thermally responsive member for moving the other of said contacts in response to changes in the temperature of the other plate, a pair of contacts for controlling energization of the means for supplying heat to the basket, a responding thermally responsive member for moving one of the last-mentioned contacts into and out of engagement with the other of the last-mentioned contacts, a heater for the responding thermally responsive member in the electrical circuit in series with the electrical heating means for the heated plate, and manually operable means for adjusting one of said last-mentioned contacts relative to the other.

5. In a clothes dryer having a basket for tumbling damp clothes to be dried, means for circulating air through the basket and means for heating the circulated air: control means for automatically terminating heating of the circulated air when the moisture content of the clothes is reduced to a preselected value, by measurement of changes in the cooling effect of the clothes upon a heated body, said control means comprising two bodies positioned to be contracted and cooled by the tumbling damp clothes said bodies being in close proximity to each other, means for electrically heating one only of said bodies, a main thermally responsive member positioned to be responsive to the temperature of the heated body, a reference thermally responsive member positioned to be responsive to the temperature of the unheated body, a pair of contacts movable into and out of engagement to energize and deenergize, respectively, the means for electrically heating the heated body, said thermally responsive members each supporting and actuating one of said contacts and being so constructed and arranged that each moves the contact actuated thereby in the same direction and to the same extent upon sensing the same change in temperature of the body to whose temperature it is responsive, a responding thermally responsive member, a

heater for said responding thermally responsive member inseries with the electrical heating means for the heated body, a pair of cooperating contacts movable into and out of engagement for controlling energization of the means for heating the circulated air, one of. the last-mentioned contacts being actuated by the responding thermally responsive member, and manually operable means for adjusting theposition of the other of said last-mentioned contacts relative to said one last-mentioned contact, whereby the control means may be a'djusted'to preselect the degree of dryness of the clothes at which the drying thereof is automatically terminated.

6. In a clothes dryer having .a basket for tumbling damp clothes to be dried, means forcirculating air through the basket and means for heating the circulated air: control means for automatically terminating heating of the circulated air when the moisture content of the clothes is reduced to a preselected value, by measurement of changes in the cooling effect of the clothes upon a heated body, said control means comprising two bodies positioned to be contacted and cooled by the tumbling damp clothes, means for electrically heating one only of said 'bodies, a main thermally responsive device so disposed as to be responsive to the temperature of the heated 'body, a reference thermally responsive device so disposed as to be responsive to the temperature of the unheated body, a pair of electrical contacts movable into and out of engagement to energize and deenergize, respectively, the means for electrically heating the heated body, said thermally responsive devices each actuating one of said contacts and being so constructed and arranged that each moves the contact actuated thereby in the same direction and to the same extent upon sensing the same change in temperature of the body to whose temperature it is responsive and the contacts disengage only when the temperature diiference of the two bodies sensed by said thermally responsive devices exceeds a predetermined value, a responding thermally responsive device, a heater for said responding thermally responsive device in series with the electrical heating means for the heated body, a pair of cooperating contacts movable into and out of engagement for controlling energization of the means for heating the circulated air, one of the lastmentioned contacts being actuated by the responding thermally responsive device, and manually operable means for adjusting the position of the other of said lastmentioned contacts relative to said one last-mentioned contact, whereby the degree of dryness of the clothes at which the drying thereof is automatically terminated may be preselected.

7. In a clothes dryer, a basket for tumbling damp clothes to be dried, means for rotating the basket about a substantially horizontal axis to tumble the clothes therein, means for circulating air through the basket, means for heating the circulated air, and control means for automatically terminating heating of the circulated air when the moisture content of the clothes is reduced to a preselected value, said control means comprising a pair of bodies rotatable with the basket and positioned so as to be contacted and cooled by the tumbling damp clothes, electrical means for supplying heat to one only of said bodies, a main bimetal associated with the heated body and responsive to the temperature thereof, a reference bimetal associated with the unheated body and responsive to the temperature thereof, each of said bimetals having a contact arm extending therefrom with the free terminal portion of one arm overlying the free terminal portion of the other arm in spaced relation thereto, an electrical contact carried by the free terminal portion of each arm for engagement one with the other to energize the heating means for the heated body, said bimetals and their respective contact arms being so constructed and arranged that the deflection thereof at the contacts is in the same direction and is equal for equal changes in temperature sensed by the bimetals and the contacts would be engaged throughout a'predetermined range of temperature difierences sensed if there were no eiTects of gravity, means providing extra Weight in one arm relative to the other arm such that gravitational force on said extra weight produces separation of the contacts once during each revolution of the basket while the temperature difference sensed by the bimetals is within the means for heating the heated body is energized, whereby 15 the responder bimetal functions in direct relation to the heat input to the heated body.

References Cited in the file of this patent UNITED STATES PATENTS 2,022,440 Slough Nov. 26, 1935 2,743,532 Steward May 1, 1956 2,820,304 Horecky Ian. 21, 1958 2,878,579 Fuchs Mar. 24, 1959 2,878,580 Hughes Mar. 24, 1959 2,885,789 Conkling et al. May 12, 195.9 2,895,230 Reiley July 21, 1959 2,999,144 Carissimi Sept. 5, 1961 Carissimi Feb. 6, 1962 

1. IN MECHANISM FOR MEASURING A CONDITION OF A MATERIAL TUMBLING IN A CONTGAINER, WHICH CONDITION AFFECTS THE HEAT ABSORPTION CHARACTERISTIC OF THE MATERIAL, TWO BODIES ADAPTED TO BE CONTACTED AND COOLED BY THE TUMBLING MATERIAL, AN ELECTRICAL HEATER FOR ONE OF THE BODIES, MEANS PROVIDING AN ELECTRICAL CIRCUIT FOR THE HEATER, MEANS FOR CONTROLLING SAID ELECTRICAL CIRCUIT INCLUDING A MAIN THERMALLY RESPONSIVE MEMBER ASSOCIATED WITH THE BODY HAVING THE HEATER AND BEING RESPONSIVE TO THE TEMPERATURE THEREOF, A REFERENCE THERMALLY RESPONSIVE MEMBER ASSOCIATED WITH THE OTHER BODY AND BEING RESPONSIVE TO THE TEMPERATURE THEREOF, COOPERATING CONTACTS CARRIED BY SAID THERMALLY RESPONSIVE MEMBERS FOR OPENING AND CLOSING SAID ELECTRICAL CIRCUIT, SAID THERMALLY RESPONSIVE MEMBERS NORMALLY MAINTAINING THE CONTACTS IN CIRCUIT-CLOSING ENGAGEMENT AND SEPARATING SAID CONTACTS ONLY WHEN THE TEMPERATURE DIFFERENCE OF THE TWO BODIES SENSED THEREBY EXCEEDS A PREDETERMINED VALUE, A RESPONDING THERMALLY RESPONSIVE MEMBER, MEANS OPERABLE BY SAID RESPONDING THERMALLY RESPONSIVE MEMBER, AND AN ELECTRICAL HEATER IN THE CIRCUIT FOR HEATING SAID RESPONDING THERMALLY RESPONSIVE MEMBER WHEN SAID CIRCUIT IS CLOSED. 